Communications systems, especially messaging and paging systems, typically operate on a channel having a specified radio frequency for a subscriber's home location. These systems are viable solutions as long as the channel and radio frequency have the spectral capacity to accommodate or provide service to all subscribers or users of the system. As the number of subscribers and the mobility of those subscribers increase, these systems may begin to experience difficulties. Adding capacity may require additional channels and radio frequencies. Assuming the demands for capacity can be met at one or another location, subscribers traveling between locations typically find that the two locations do not share a common radio frequency or channel. These subscribers may be required to carry and maintain a messaging unit or pager for each of the locations the subscriber might be traveling to, or one pager that can be adjusted to each local channel. This is a constraint and significant inconvenience for subscribers that need messaging or paging coverage in multiple locations.
As subscribers demanded messaging and paging service in multiple areas, practitioners sought solutions that provided the subscriber the ability to move between paging areas and have the convenience of carrying a single subscriber unit. This demand and these concerns spawned the concept of roaming in the paging industry or for paging systems. Roaming relates to the ability of a subscriber to have service in a paging area known as a home area, and additionally have the option of temporarily extending this service outside of the home area.
Messages for the subscriber are ordinarily sent by the home system on the home system channel and radio frequency to the subscriber. When a subscriber knows they will be traveling out of the home area, they contact the service provider via telephone to advise the provider as to when and where the subscriber expects to travel. With this information the service provider forwards messages for the subscriber to those areas being visited during the times agreed upon. Capacity on the home system and other areas is not wasted as the message need not be broadcast in the home area or other areas when the service provider knows the subscriber is not present.
Messaging units operating on multiple frequencies have been built. These multiple frequencies represent valid frequencies in various paging systems and allow the messaging unit to operate in or roam to systems with different frequencies; however the messaging unit needs to be tuned, typically manually, to the proper channel. The concept of roaming relies on the cooperation and coordination of both the service provider or system and the subscriber or unit to ensure the continuity of service over multiple service areas for specified periods of time. Prior art has provided for roaming that included coverage within the home area and roaming areas by ensuring that messages are sent to all the different coverage areas the subscriber might be located in at least during the apparent roaming times, but this may waste system capacity.
Potential issues arise when the subscriber can receive channels from more than one system, such as the home system and either one or more roaming or other systems at the same time. The system inefficiently uses airtime by sending duplicate messages to multiple controllers or systems, or alternatively messages may be missed if the messaging unit is tuned to a channel other than the channel the system is using. Also, if the messaging unit has scanning capability, the unit can waste valuable battery resources scanning multiple systems attempting to determine the most appropriate channel to tune to.
Roaming systems suitable to mitigate some of these issues have been proposed by Gaskill, et al. U.S. Pat. No. 4,897,835. Gaskill et al. suggests that the messaging system tells the messaging unit to tune to a particular channel. Subsequent messages are broadcast only on that channel frequency. Drawbacks to Gaskill include sending the tuning message on all channels the messaging unit may be on, thus wasting capacity, and the possibility that the messaging unit does not receive the tuning message thus missing subsequent messages.
Clearly a need exists to automatically allow a system and a messaging unit to adequately and routinely modify and effect the operating channels available to subscribers.